U.S. Pat. No. 6,920,799 B1 discloses a magneto-inductive, flow measuring device, with which it is possible to suppress corrosive degradation of a reference electrode. This known remedy assumes, that the reference electrode is usually in direct contact with the medium. If an electrical current flows through the reference electrode, then this leads, as a result of electrolysis, to corrosion on the reference electrode. This is, naturally, highly undesirable. In order to limit the electrical current flowing through the reference electrode, this patent proposes to connect a limiter resistance after the reference electrode. The patent recommends, thus, a remedy, in the case of which an electrical current flowing through the reference electrode is lowered, without taking into consideration, or removing, the cause of the electrical current flow. A corrosive degradation of the measuring electrodes remains unrecognized; as a result, a corrosion of the measuring electrodes is also not counteracted. While, in the case of this known remedy, danger of corrosion of the reference electrode is reduced, a high-resistance, reference potential results, due to the after-connected, relatively large resistance, and this means that stability and reproducibility of the measured values can significantly worsen.